Device and method for protecting memory data against illicit access

Abstract

An electronic device for storing protected data is disclosed. The electronic device includes memory protection logic operable to interface with memory, such as non-volatile ROM for storing protected data therein. The protected data in one embodiment is program code. The access to the protected data is restricted by a local processor, such as a microcontroller or microprocessor for execution thereon within the electronic device. Further, the electronic device includes validation logic operative in a first mode, for checking the validity of the data and for producing a validity signal, such as a checksum, enabled to determine whether that data is valid. In order to prevent access to intermediate validity calculations which may allow an individual to gain knowledge of the protected data, a validity signal output control is provided for inhibiting an output of the validity signal to outside the device until the validity of a predetermined quantity of the protected data has been checked. This predetermined quantity is made sufficiently large and preferably equal to all of the protected data. In another embodiment, a reset for setting the contents of the validity signal if the checking is interrupted is also included.